Query DataTable column into List (or Array) of Integers

Question

I'm trying to query a DataTable to get the list of ID's (integers) that correspond to a specific criteria, such that I can then parse that list into a joined string that can be used as a filter on a DataView :

Dim dvFilteredList As New DataView(dtbList)
Dim existingSelections = (From dtr In dtbMain.AsEnumerable
                          Where dtr.Field(Of String)("Field1") = strField1Value _
                              And dtr.Field(Of String)("Field2") = strField2Value _
                              And dtr.Field(Of String)("Field3") = strField3Value _
                              And Not IsDBNull(dtr.Field(Of Integer)("SomeID"))
                          Select New With {.SomeID = dtr.Field(Of Integer)("SomeID")}).ToList
Dim strViewFilter As String = "[SomeID] NOT IN (" & String.Join(",", existingSelections) & ")"
dvFilteredList.RowFilter = strViewFilter

When I try to query the list of integer ID's into existingSelections, I get this exception :

Cannot cast DBNull. Value to type 'System.Int32'. Please use a nullable type.

How can I query the qualifying ID's into a list (or array) that I can then parse?

Answer 1

The Field extension method supports nullable types, so use it correctly:

AndAlso dtr.Field(Of Integer?)("SomeID").HasValue

(also use AndAlso instead of And everywhere for performance reasons)